Fullstack Software Engineer in London

Meet Siena. Siena is the first intelligence layer for customer experience. We are creating an operating system of AI agents that learn, remember, and act across every customer touchpoint—from support conversations to shopping experiences to voice and social media interactions. Siena doesn’t just automate support; it powers shopping agents, builds persistent customer memory, generates actionable business insights, and creates empathetic interactions that feel human. We are transforming how businesses understand and connect with their customers, turning every interaction into intelligence that makes the next one better.

The team is a small, distributed team that punches way above our weight. Every person here has outsized impact because we’ve built leverage into everything we do. This philosophy makes us faster and, frankly, more fun to work with. If you’re excited about building something that doesn’t exist yet, keep reading. We’re building agents that don’t just respond to customers—they remember them, learn from every interaction, and connect experiences across channels.

About The Role: As a fullstack engineer at Siena, you’ll own projects end-to-end, developing and optimizing features within our AI-powered customer support automation platform. You’ll work closely with product, shaping our roadmap while building reliable, high-performance systems. Your code will power millions of monthly customer interactions across global brands, where reliability and speed directly impact business outcomes. If you love solving real-world problems, thrive in fast-paced environments, and take pride in shipping great products, this role is for you.

What You’ll Do:

• Design, build, and maintain scalable features across the full stack (frontend, backend, and infra).
• Collaborate with Product to break down scope into iterative, high-impact releases.
• Integrate cutting-edge LLM capabilities into real enterprise workflows.
• Work on an AI-first product, integrating cutting-edge LLM capabilities into enterprise customer support workflows.
• Solve complex engineering challenges, from optimizing API performance to refining microservices architecture.
• Maintain and improve our cloud infrastructure (AWS) with a DevOps mindset.
• Exercise high agency and ownership—taking initiative, making decisions, and driving ideas to production.

Who You Are:

• 3+ years building in React, TypeScript, and Express.
• Strong with PostgreSQL, Redis, and cloud environments (AWS: Fargate, Lambda, EC2, SQS).
• Familiar with CI/CD (CodePipeline, GitHub Actions, or similar).
• Experience with microservices and scalable systems.
• Product-driven—you care about the impact of what you ship, not just the code.
• AI-first—you live in Cursor, Claude Code and are comfortable orchestrating coding agents.
• Naturally curious and proactive; you don’t wait for instructions, you create momentum.

Bonus points for:

• Python, or event-driven architectures.
• Infra-as-code (Terraform, CDK).
• Experience integrating with LLMs in production.
• Event-driven architecture experience.

Why Siena?

• Meaningful impact. Your work directly shapes our product and company.
• Globally distributed team working at the bleeding edge of CX and AI.
• Great salary plus the opportunity for equity or stock grants.
• Learning budget. If you’re growing, so are we.
• The thrill of building something new. Join us at a stage where your contributions matter most.
• AI-fluency. Make AI your second nature.
• Tackle unsolved problems. We’re redefining how customer experience will look like in the next decades.

Our values: The people who thrive here are curious, customer-obsessed, and take ownership without being asked. They fix problems first and explain later. They’re direct about feedback—both giving and receiving it—because they care more about getting things right than being polite. They maintain high standards while moving at startup speed, and they build real relationships with teammates because they know that’s how great work gets done. When things get tough, they adapt and keep pushing forward.

Our approach to AI: The people who thrive here treat AI like a natural extension of themselves. They’ve built their own ecosystem of agents - some for research, others for debugging, writing, analysis, or writing code. They know which AI works best for what problem. Everyone gets premium accounts (ChatGPT, Claude, Perplexity Pro, Cursor, Lovable) plus a quarterly budget for new tools. But the magic happens in how we share knowledge. Demo days where someone shows off clever workflows. Slack threads about which model handles a specific use case better. Learning from each other’s AI workflows.

At Siena, we’re not just looking for people who can do a job. We’re looking for people who want to break boundaries, create the future, and reshape industries. If that’s you, we look forward to your application.

Siena provides equal employment opportunities to all employees and applicants for employment without regard to race, color, religion, sex, national origin, age, disability, genetics, sexual orientation, gender identity, or gender expression. We are committed to a diverse and inclusive workforce and welcome people from all backgrounds, experiences, perspectives, and abilities.